This autumn and early winter will see the biggest change in Chicago's Museum Campus since Lake Shore Drive took a hard swing to the west to create the parkland connection of cultural institutions 14 years ago.

This time, though, the alteration is not one of roadways and dirt piles, but of people.

John McCarter and Paul Knappenberger, presidents of the Field Museum of Natural History and the Adler Planetarium, respectively, are stepping down after a combined 37 years of service.

The two men, both in their early 70s, have much else in common. Each has remade his institution, building large, new additions and theaters and bringing virtually all of the gallery space up to modern standards. Each has fought to get high-profile pieces in the collections, with the Field landing Sue the T. rex at the end of the last century, and the Adler more recently getting spurned by NASA in its bid to house a retired space shuttle.

Although McCarter came to his post in 1996 from a business background and Knappenberger to his in 1991 from science and the museum world, each has ensured a commitment to science backstage, in the places the public doesn't see.

And, yes, each has overseen admission price hikes, in Knappenberger's case the first entry fee at the Adler, which, he says, has been remade on his watch from a cozy planetarium into a well-rounded space museum that pioneered the concept of having research astronomers on staff.

"I like to push the envelope," Knappenberger says. "I can see what others are doing, and I want the Adler to be out front. And because we have on our staff scientists and a Space Visualization Laboratory, we have the resources to really be the leading — and are at this point — the leading planetarium in the world. We have certainly the most technologically advanced theater. We've got now, I think, the strongest production staff of any planetarium."

McCarter, meanwhile, takes credit for, along with staff, helping reshape the Field's mission to suit the times: incorporating molecular biology into scientific research; digitizing the specimen collection; pioneering aggressive, innovative conservation work abroad and in the Midwest; and bringing in blockbuster exhibits as well as ones on such hot-button issues (in some circles) as evolution and climate change.

"The presence and impact of evolution over, you know, billions of years is irrefutable," McCarter says, and the museum's spectacular Evolving Planet permanent exhibition, opened in 2006, backs him up. "This is at the core. This is like gravity. This happened, and we are telling that story. And I've been cautioned to be very cautious. … I don't have any reluctance to grapple with evolution or with climate change."

McCarter's successor, former University of Oregon President Richard Lariviere, is at the Field, getting the Grand Tour from the man he'll replace on Oct. 1. Knappenberger will be in command until the end of the year, with no successor yet named. That announcement could come, Adler staff anticipate, later this month.

Because running two such prominent cultural institutions is, in a way, a public trust, we thought it fitting to conduct, separately, a sort of exit interview with both men, touching on their transformative tenures, the challenges facing museums in the 21st century and what they may have left undone.

What follows are edited excerpts from those conversations.

On the space shuttle that got away, and the dinosaur that didn't:

Knappenberger: We wanted it badly. The point we made was NASA is largely on the coasts, and wouldn't it be great for the kids that lived in the middle of the country to have access to one of the shuttles? And if you're going to do that, Chicago is an obvious choice. As I look at it now, one had to go to Washington, to (the National Air and Space Museum), and I think (NASA administrator) Charlie Bolden wanted one to go to the Kennedy Space Center (in Florida). That only left one other, and then the Enterprise. So he took the two largest cities, New York and LA, and that's where they went. I think there were a lot of stronger proposals than either New York or Los Angeles. Even if you set Chicago aside, Seattle had a very strong proposal, as did Dayton and Houston. So I don't know. At least we got the space shuttle flight simulator, which will be fine once that thing gets up and running here.